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Securing the Superpowers - Who loaded that eBPF program?

This repository contains the demo and the corresponding instructions that was presented at SecurityCon 2023 NA, Seattle during Securing the Superpowers - Who loaded that eBPF program?.

Environment

Create a GKE cluster:

export NAME="$(whoami)-$RANDOM"
gcloud container clusters create "${NAME}" \
  --zone europe-central2-a \
  --num-nodes 1

Deploy Tetragon:

helm repo add cilium https://helm.cilium.io
helm repo update
helm install tetragon cilium/tetragon -n kube-system
kubectl rollout status -n kube-system ds/tetragon -w

Apply a TracingPolicy which would detect BPF program loading and BPF map creation:

kubectl apply -f bpf.yaml

Demo 1 - Who loaded that simple BPF program? And created the map?

Create washington namespace:

kubectl create ns washington
namespace/washington created

Apply seattle-bpf-droid pod on washington namespace:

kubectl apply -f seattle-bpf-droid.yaml -n washington
pod/seattle-bpf-droid created

Wait until the seattle-bpf-droid pod is ready:

kubectl get pods -n washington
NAME                READY   STATUS    RESTARTS   AGE
seattle-bpf-droid   1/1     Running   0          32s

The seattle-bpf-droid pod is doing 2 main instructions periodically, in every 30s:

  1. Loading a BPF program
  2. Creating a BPF map

Detecting BPF program loading

Start observing the logs from the seattle-bpf-droid pod:

kubectl exec -it -n kube-system tetragon-nljct -c tetragon -- /bin/bash
tetra getevents -o compact -pod seattle-bpf-droid

The pod is loading a seattle_bpf_prog.o BPF program with kprobe type in every 30s with bpftool, which can be seen by the following events:

🚀 process washington/seattle-bpf-droid /usr/local/bin/bpftool prog load seattle_bpf_prog.o /sys/fs/bpf/a85d485007 --legacy type kprobe
🐝 bpf_check washington/seattle-bpf-droid /usr/local/bin/bpftool BPF_PROG_TYPE_SOCKET_FILTER  instruction count 2
🐝 bpf_check washington/seattle-bpf-droid /usr/local/bin/bpftool BPF_PROG_TYPE_SOCKET_FILTER test instruction count 2
🐝 bpf_check washington/seattle-bpf-droid /usr/local/bin/bpftool BPF_PROG_TYPE_KPROBE amazing_func instruction count 2
💥 exit    washington/seattle-bpf-droid /usr/bin/sleep 30s 0

To be able to detect BPF program loading, Tetragon hooks into the bpf_check function which represents the Verifier check during the program load. This is performed everytime a BPF program is loaded. The BPF_PROG_TYPE_KPROBE represents the program type, the amazing_func represents the function name and the instruction count 2 tells how many instructions the specific program contain.

The program type can be also BPF_PROG_TYPE_SOCKET_FILTER, BPF_PROG_TYPE_XDP etc. We will see examples for those later.

Detecting BPF map creation

The pod is also creating a tetragon_bpf_5016 BPF map and pin it to /sys/fs/bpf/seattle_5016 location by using bpftool. We can see that the map was hash map (BPF_MAP_TYPE_HASH), the key and the value size were 4 and the max entries were 4 as well.

🚀 process washington/seattle-bpf-droid /usr/local/bin/bpftool map create /sys/fs/bpf/seattle_5016 type hash key 4 value 20 entries 4 name tetragon_bpf_5016
🐝 bpf_check washington/seattle-bpf-droid /usr/local/bin/bpftool BPF_PROG_TYPE_SOCKET_FILTER  instruction count 2
🗺 bpf_map_alloc washington/seattle-bpf-droid /usr/local/bin/bpftool BPF_MAP_TYPE_HASH tetragon_bpf_50 key size 4 value size 20 max entries 4
💥 exit    washington/seattle-bpf-droid /usr/local/bin/bpftool map create /sys/fs/bpf/seattle_5016 type hash key 4 value 20 entries 4 name tetragon_bpf_5016 0

To be able to detect BPF map creation, Tetragon hooks into the security_bpf_map_alloc function which is called during a BPF map create.

Demo 2 - Which programs were loaded by Cilium?

As a second demo, we will show a real use case and detect what BPF programs were loaded by Cilium and what BPF maps were created.

Create cilium namespace:

kubectl create ns cilium
namespace/cilium created

Set the NAME and ZONE variables to your cluster:

NAME=<cluster_name>
ZONE=<zone_name>

Extract the cluster CIDR to enable native routing:

NATIVE_CIDR="$(gcloud container clusters describe "${NAME}" --zone "${ZONE}" --format 'value(clusterIpv4Cidr)')"
echo $NATIVE_CIDR

Install Cilium via helm:

helm install cilium cilium/cilium --version 1.12.5 \
  --namespace kube-system \
  --set nodeinit.enabled=true \
  --set nodeinit.reconfigureKubelet=true \
  --set nodeinit.removeCbrBridge=true \
  --set cni.binPath=/home/kubernetes/bin \
  --set gke.enabled=true \
  --set ipam.mode=kubernetes \
  --set ipv4NativeRoutingCIDR=$NATIVE_CIDR

Start observing the events from the Cilium pod:

tetra getevents -o compact --pod cilium

Restart the Cilium agent:

 kubectl delete pods -n cilium cilium-xpw8x
pod "cilium-xpw8x" deleted

An example piece:

🚀 process cilium/cilium-xpw8x /usr/local/bin/tc filter replace dev lxc_health ingress prio 1 handle 1 bpf da obj 471_next/bpf_lxc.o sec from-container
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SOCKET_FILTER  instruction count 2
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SOCKET_FILTER  instruction count 2
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SOCKET_FILTER test instruction count 2
🗺 bpf_map_alloc cilium/cilium-xpw8x /usr/local/bin/tc BPF_MAP_TYPE_PROG_ARRAY cilium_calls_00 key size 4 value size 4 max entries 33
🗺 bpf_map_alloc cilium/cilium-xpw8x /usr/local/bin/tc BPF_MAP_TYPE_PERCPU_ARRAY cilium_tail_cal key size 4 value size 48 max entries 1
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_CGROUP_SOCK  instruction count 2
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS __send_drop_not instruction count 45
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS tail_handle_ipv instruction count 1383
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS tail_ipv4_ct_eg instruction count 698
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS tail_handle_ipv instruction count 1139
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS tail_handle_arp instruction count 190
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS handle_xgress instruction count 86
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS tail_ipv4_to_en instruction count 1224
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS tail_ipv4_ct_in instruction count 697
🐝 bpf_check cilium/cilium-xpw8x /usr/local/bin/tc BPF_PROG_TYPE_SCHED_CLS handle_policy instruction count 1870
💥 exit    cilium/cilium-xpw8x /usr/local/bin/tc filter replace dev lxc_health ingress prio 1 handle 1 bpf da obj 471_next/bpf_lxc.o sec from-container 0